(function ( doc, win ) {
  var docEl = doc.documentElement,
    resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
    recalc = function () {
      var clientWidth = docEl.clientWidth;
      if ( !clientWidth ) return;
      if ( clientWidth >= 640 ) {
        docEl.style.fontSize = '100px';
      } else {
        docEl.style.fontSize = 100 * ( clientWidth / 640 ) + 'px';
      }
    };

  if ( !doc.addEventListener ) return;
  win.addEventListener( resizeEvt, recalc, false );
  doc.addEventListener( 'DOMContentLoaded', recalc, false );
  //recalc()
})( document, window );
